DermNet NZ

Cellulitis

What is cellulitis?

Cellulitis is a common bacterial infection of the skin, which can affect all ages. It usually affects a limb but can occur anywhere on the body. Symptoms and signs are usually localised to the affected area but patients can become generally unwell with fevers, chills and shakes (bacteraemia).

If there is no increased warmth over the skin it is unlikely to be cellulitis.

Lymphangitis is a red line originating from the cellulitis and leading to tender swollen lymph glands draining the affected area (eg in the groin with a leg cellulitis). It is caused by infection within the lymph vessels.

After successful treatment, the skin may flake or peel off as it heals.

Abscess

Cellulitis

What may cause cellulitis?

Cellulitis is caused by bacterial infection. It can occur by itself, or complicate an underlying skin condition or wound. The most common infecting organisms are Streptococcus pyogenes (two thirds of cases) and Staphylococcus aureus (one third). Rare causes of cellulitis include:

Pseudomonas aeruginosa, particularly following a puncture wound involving the foot or hand

How is the diagnosis made?

The diagnosis of cellulitis is based on the clinical features. If any pustules, crusts or erosions are present, a swab should be taken for culture. A complete blood count is likely to show leukocytosis (raised white cell count). Elevated C-reactive protein is usual. Blood cultures may be of use if a patient has a high fever or is otherwise very unwell.

Occasionally further investigations are required to rule out other possible diagnoses such as deep vein thrombosis of the leg, radiation damage following radiotherapy, or inflammatory breast cancer (carcinoma erysipeloides).

Oral antibiotics used commonly are penicillin, flucloxacillin, dicloxacillin, cefuroxime or erythromycin. The usual intravenous antibiotics used are penicillin-based antibiotics (eg penicillin G or flucloxacillin) or cephalosporins (eg cefotaxime, ceftriaxone or cefazolin) for a few days. Sometimes oral probenecid is added to maintain antibiotic levels in the blood. Knowledge of local organisms and resistance patterns is essential in selecting appropriate antimicrobial therapy.

Most patients can be treated with oral antibiotics at home, usually for 5 to 10 days. However if there are signs of systemic illness or extensive cellulitis, treatment may require intravenous antibiotics either as an outpatient or in hospital. Treatment for uncomplicated cellulitis is usually for 10 to 14 days but antibiotics should be continued until all signs of infection have cleared (redness, pain and swelling) – sometimes for several months.

Oral antibiotics used commonly are penicillin, flucloxacillin, dicloxacillin, cefuroxime or erythromycin. The usual intravenous antibiotics used are penicillin-based antibiotics (eg penicillin G or flucloxacillin) or cephalosporins (eg cefotaxime, ceftriazone or cefazolin) for a few days. Sometimes oral probenecid is added to maintain antibiotic levels in the blood.

In situations where a broader antibiotic cover is required, for example a diabetic patient with a foot ulcer complicated by cellulitis, amoxicillin and clavulanic acid may be used. Clindamycin, sulfamethoxazole/trimethoprim, doxycycline and vancomycin are alternative antibiotics in patients with serious penicillin or cephalosporin allergy, or where infection with methicillin-resistant Staphylococcus aureus is suspected.

What should I do if I have recurrent cellulitis?

Patients with recurrent cellulitis should

Avoid trauma, wear long sleeves and pants in high risk activities eg gardening